The man, in his 30s, was the subject of intense media speculation surrounding his visit to the UK, which culminated in him flying out of London the day before the attacks. His presence in the country, apparently unmonitored, led to criticism of MI5.

However, The Independent has learnt that the man had no role in the attacks. Inquiries in the past week have discovered that the man was an innocent Pakistani traveller who had a similar name to an al-Qa'ida terrorist who was on a watch list of several foreign security agencies.

A similar mix-up is understood to be behind the claims by US intelligence that Germaine Lindsay, 19, the bomber who carried out the King's Cross attack, was on a British watch list. This was because the "fourth" bomber was wrongly identified in the United States as Lindsay Jermaine - someone with a similar name to a terrorist suspect.

Scotland Yard is concentrating on establishing the movements of the four bombers from Leeds and Aylesbury, and what explosives they used.

Sniffer dogs are being used on the Tube to detect explosives. Dozens of dogs will be deployed throughout the London Underground system and the police may also introduce random checks using metal and bomb detectors on the Underground.

* Police have until Saturday to continue questioning a 29-year-old man arrested in West Yorkshire last week in connection with the bombings. He is the only person to have been arrested so far in Britain over the attacks.

A man widely reported to have slipped into Britain to "mastermind" the London bombings was an innocent Pakistani who happened to have a similar name to a suspected al-Qa'ida leader.

The man, in his 30s, was the subject of intense media speculation surrounding his visit to the UK, which culminated in him flying out of London the day before the attacks. His presence in the country, apparently unmonitored, led to criticism of MI5.

However, The Independent has learnt that the man had no role in the attacks. Inquiries in the past week have discovered that the man was an innocent Pakistani traveller who had a similar name to an al-Qa'ida terrorist who was on a watch list of several foreign security agencies.

A similar mix-up is understood to be behind the claims by US intelligence that Germaine Lindsay, 19, the bomber who carried out the King's Cross attack, was on a British watch list. This was because the "fourth" bomber was wrongly identified in the United States as Lindsay Jermaine - someone with a similar name to a terrorist suspect.

Scotland Yard is concentrating on establishing the movements of the four bombers from Leeds and Aylesbury, and what explosives they used.

Sniffer dogs are being used on the Tube to detect explosives. Dozens of dogs will be deployed throughout the London Underground system and the police may also introduce random checks using metal and bomb detectors on the Underground.

* Police have until Saturday to continue questioning a 29-year-old man arrested in West Yorkshire last week in connection with the bombings. He is the only person to have been arrested so far in Britain over the attacks.